# Why (N+1)sec's mDP Implementation does not check whether all the XORED received $z$ values are 0

In the original mDP protocol once all $$z$$ values received from each participant the following calculation is being done:

If either $$XOR(z_1,z_2,...,z_n) = 0$$ or received invalid Signature then abort the the key computation. Else $$z'_{j,j+1} = XOR(z'_{j_j-1},z'_{j})$$

And the final Key will be: $$k_i=H_g(z'_{1,2},\ldots,z'_{n,1},sid_i)$$

But on the approach used (N+1)sec of the algorithm above the check $$XOR(z_1,z_2,...,z_n) = 0$$ is not performed thus I want to ask why in (N+1)sec this check is omitted?

Also I attempted to implement the key agreement, thus I want to ask in what conditions/requirements do I need so I can omit the check $$XOR(z_1,z_2,...,z_n) = 0$$ as well?